title: Retinoic acid production by endocardium and epicardium is an injury response essential for zebrafish heart regeneration.
abstract: Zebrafish heart regeneration occurs through the activation of cardiomyocyte proliferation in areas of trauma. Here, we show that within 3 hr of ventricular injury, the entire endocardium undergoes morphological changes and induces expression of the retinoic acid (RA)-synthesizing enzyme raldh2. By one day posttrauma, raldh2 expression becomes localized to endocardial cells at the injury site, an area that is supplemented with raldh2-expressing epicardial cells as cardiogenesis begins. Induced transgenic inhibition of RA receptors or expression of an RA-degrading enzyme blocked regenerative cardiomyocyte proliferation. Injured hearts of the ancient fish Polypterus senegalus also induced and maintained robust endocardial and epicardial raldh2 expression coincident with cardiomyocyte proliferation, whereas poorly regenerative infarcted murine hearts did not. Our findings reveal that the endocardium is a dynamic, injury-responsive source of RA in zebrafish, and indicate key roles for endocardial and epicardial cells in targeting RA synthesis to damaged heart tissue and promoting cardiomyocyte proliferation.
authors.affiliation: Department of Cell Biology and Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Kazu
authors.initials: K
authors.lastname: Kikuchi
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Holdway
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Major
authors.forename: Nicola
authors.initials: N
authors.lastname: Blum
authors.forename: Randall D
authors.initials: RD
authors.lastname: Dahn
authors.forename: Gerrit
authors.initials: G
authors.lastname: Begemann
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Poss
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D005075:Biological Evolution; D049109:Cell Proliferation; D004699:Endocardium / Q000166:cytology / Q000293:injuries / Q000378:metabolism*; D006321:Heart / Q000033:anatomy & histology / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D032383:Myocytes, Cardiac / Q000166:cytology / Q000502:physiology; D010496:Pericardium / Q000166:cytology / Q000293:injuries / Q000378:metabolism*; D012038:Regeneration / Q000502:physiology*; D050697:Retinal Dehydrogenase / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D014212:Tretinoin / Q000378:metabolism*; D015027:Zebrafish / Q000033:anatomy & histology / Q000502:physiology*; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D029961:Zebrafish Proteins; D014212:Tretinoin; C518907:Aldh1a2 protein, zebrafish; D050697:Retinal Dehydrogenase